AER2: Lift

Question 1

Define Camber

Answer 1

The maximum distance between the chordline and the mean camber line

Question 2

Define Chordline

Answer 2

A straight line running from the leading edge to the trailing edge of the wing.

Question 3

Define Mean Camber line

Answer 3

Line marking the middle of the wing, taking into account the curve of the aerofoil.

Question 4

Define relative airflow

Answer 4

The relative direction and speed of the air before it is influenced by the presence of an aircraft. Always equal and opposite to the flight path.

Question 5

Define Angle of Attack

Answer 5

The angle between the chordline of the wing and the relative airflow.

Question 6

Define Air density

Answer 6

Is the mass of the air per unit of volume (Mass/Volume). Is given the greek letter (p) or rho.

Question 7

Define the aerofoil section

Answer 7

The wing of the aircraft, produces more lift than drag with a streamline rounded leading edge and sharp trailing edge.

Question 8

Define Static pressure

Answer 8

Pressure due to molecular motion at rest and atmospheric pressure.

Question 9

Define Dynamic pressure

Answer 9

Pressure caused due to motion

Question 10

Define total air pressure

Answer 10

Static plus dynamic is total air pressure.

Question 11

Define Bernoulli’s theorem and explain how this relates to a wing.

Answer 11

In a duct, when airflow is accelerated, static pressure drops. This is seen on a wing, when the relative airflow over the top of the wing is accelerated, producing Low pressure over the top of the wing. The airflow underneath the wing is not accelerated, producing a High pressure system underneath. This produces lift.

Question 12

Define Co - efficient of lift

Answer 12

The aircraft’s ability to produce lift. (via the aerofoil).

Question 13

What is the Co - efficient of lift affected by?

Answer 13

• Aerofoil shape (constant)
• Angle of attack (not constant) as this increases, so too does the value of cL.
  Aerofoil surface area (constant)
  (think about the equation!)

Question 14

What is the name of the maximum angle of attack?

Answer 14

The critical angle. Exceed this and you will stall the aircraft.

Question 15

What happens generally when you increase the angle of attack?

Answer 15

There will be an increase in the curvature of the aerofoil, an increase therefore in the airflow acceleration over the top of the wing, and an increase in the pressure on the top of the wing. Lift will as a result increase also.

Question 16

What is the equation for lift?

Answer 16

L = cL x p x v2 x S
2

Where: 
L = Lift
p = rho (air density)
cL = co - efficient of lift
v = Airspeed
s = Surface area of the wing.

Question 17

Define centre of pressure

Answer 17

Is the point on the chordline through which the total aerodynamic reaction is considered to act. (lift and drag)

Question 18

Define total reaction

Answer 18

The resultant of all aerodynamic forces acting on the wing of the aircraft.

Question 19

Identify some lift/drag devices of an aircraft

Answer 19

Flaps, slats, slots, spoilers, speed brakes.

Question 20

Define Flaps

Answer 20

Alter the camber of the wing and can lengthen the chordline to produce more lift.

Question 21

Define Slats/Slots

Answer 21

Aerofoils attached to the leading edge of the wing, provides an energised air channel that activates the upper layer of the wing, increases lift at high angles of attack. Slots provide a corridor for air to pass through under the slat.

Question 22

Define Spoilers and speed brakes

Answer 22

Spoilers are located on wings and ‘spoil’ the airflow over the upper surface, increasing drag and reducing lift. Speed brakes are located in many places (think F-15). Increase drag.

Question 23

Define stalling

Answer 23

Stalling occurs when there is a breakdown of streamlined airflow over the upper surface of the wing. The turbulent air no longer produces the decreased pressure on the top of the wing and lift is decreased as a result. This is the critical angle/Stall angle.

Question 24

Recovery from Stalling

Answer 24

Attitude down, increase speed.

Question 25

Define centre of pressure

Answer 25

The point, usually on the chordline, through which the total reaction is considered to act.

Question 26

Define centre of gravity of the aircraft

Answer 26

The point of balance where the total weight of the aircraft acts through.